This invention relates broadly to sterilization of medical devices by ultraviolet radiation. More specifically, this invention relates to a sterilization system by which the amount of radiation produced by the sterilization system is measured, and to the method of measuring and controlling the amount of radiation produced by the sterilization system.
Medical device sterilization processes and in particular commercial contact lens manufacturing sterilization processes typically involve some form of temperature and/or pressure-based sterilization techniques. For example, a hydrophilic contact lens is typically first formed by injecting a monomer mixture into a mold. The monomer mixture is then polymerized (i.e. the lenses are cured). After other optional processing steps, such as quality inspections, the lens is placed in a container with a solution and the container is sealed. The packaged lens is sterilized by placing the container in an autoclave at an elevated humidity, temperature and pressure for an extended period of time, usually at least 15 minutes, and more typically 30 minutes. Although this commercial process produces thoroughly sterilized contact lenses, the batch-wise autoclave sterilization step is time consuming, costly, and inefficient.
European Patent Application No. 0 222 309 A1 discloses a process using ozone, in which packaging material is disinfected in a manufacturing setting. The process involves feeding an oxygen stream into an ozonating chamber, generating ozone from oxygen in the ozonating chamber, placing packaging containers in a sanitizing chamber, feeding the ozone into the sanitizing chamber, and purging the ozone from the sanitizing chamber with sterile air. The process requires that the ozone contact the packaging material for a predetermined time, followed by the sterile air purge step. The process is offered as an alternative to heat-steam sterilization, sterilization by application of electromagnetic radiation, or chemical agent sterilization.
U.S. Pat. No. 5,618,492 discloses a process for producing a sterile contact lens in a sealed container during a continuous production process wherein the contact lens is immersed in an ozone-containing solution within a container during a continuous lens packaging process, and the lens and container are subsequently subjected to ultraviolet radiation primarily to degrade the ozone. This process sterilizes the contact lens and the container.
U.S. Pat. No. 4,464,336 teaches a method of sterilization using a flash discharge ultraviolet lamp, which produces a very large instantaneous output, which is capable of deactivating microorganisms, including Aspergillus niger. 
U.S. Pat. Nos. 5,034,235 and 4,871,559 disclose the use of intermittent pulses of very intense, very short duration pulses of light in the visible and near visible frequencies to inactivate microorganisms on the surface of food products, and suggest that the method can be used for packages, medical devices, and food products in packages.
U.S Pat. No. 5,786,598 discloses the idea of using a flash lamp system to sterilize contact lenses in a preserved solution in a container, however, there are no conditions defined to accomplish sterility, nor examples which show that sterility can be accomplished.
U.S. Pat. No. 4,629,896 discloses an apparatus for monitoring the intensity of a UV source (for example, a water sterilizer) in which there is an optical detection unit which detects uv radiation and converts that radiation into an electrical signal, so that the intensity of the radiation can be monitored, and when it falls below a certain level the lamp can be shut off.
WO 97/43915 discloses the use of pulsed light to deactivate microorganisms in a contact lens container. Further, it discloses a method of receiving a portion of the pulsed light, generating an output signal in response to the portion of pulsed light received, and determining whether the pulse of light is sufficient to effect a prescribed level of deactivation of microorganisms in the target area. WO 97/43915 discloses that the fluence-per-flash or the spectral content of the flashes can be measured for various regions of the spectrum by using filters. There are long lists of possible pieces of equipment which might be incorporated into the measuring device, but no embodiment or example of such a device is described. WO 97/43915 suggests the use of an ultraviolet calorimeter to measure the energy in a light pulse, and states that it is traceable to international standards; however, an ultraviolet calorimeter only provides a linear response to a specific pulsewidth, specific wavelength and specific intensity of light, and therefore is only traceable to international standards within those specified parameters. Outside of those specified parameters the ultraviolet calorimeter typically has a non-linear response which is not traceable back to the calibration set-up for which there are international standards. Further, it is not appropriate to use an ultraviolet calorimeter to calibrate a photodetector to international standards. An ultraviolet calorimeter only provides a single measurement of the total energy in the ultraviolet range, and does not provide any spectral information. The measurement it provides is an uncalibrated, relative output based upon the pulsed light energy, multiplied by the responsivity of the detector, and multiplied by the bandpass and spatial filtration of the filter which provides the only radiation to the calorimeter. Further, the calorimetric sensor must have a rest period of a minimum of ten seconds between pulses since it is a thermal sensor. If the ultraviolet calorimeter were used to provide instantaneous and in-line monitoring, the process of sterilizing using pulsed light sterilization would be either ineffective or so slow, it would not be desirable.
There still remains a need for a time-efficient, continuous in-line, and cost effective sterilization system comprising a monitoring and control system and method of sterilization for products, particularly medical products, which can be used in the production line and which can measure and control the radiation to assure that every product is sterilized.
This invention provides a sterilization system comprising: a radiation source, and a monitoring system comprising a sensor; and a timing means; wherein the measurement of energy by said sensor is substantially synchronized based on said timing means to the start and end of a pulse of radiation from said radiation source or to the start and end of the exposure of a product to said radiation.
This invention further provides a method of measuring energy within a sterilization system wherein said sterilization system comprises a radiation source, and a monitoring system comprising a sensor, and a timing means, comprising the step of:
substantially synchronizing based on said timing means the measurement of energy by said sensor to the start and end of a pulse of radiation from said radiation source or to the start and end of the exposure of a product to said radiation.
This invention further provides a method of monitoring energy of a sterilization system wherein said system comprises a radiation source, and a monitoring system comprising a sensor, and a timing means, comprising the step of:
substantially synchronizing based on said timing means the measurement of energy by said sensor to the start and end of a pulse of radiation from said radiation source or to the start and end of the exposure of a product to said radiation.
The sensor is preferably an optical or electrical sensor or both. The optical sensor measures the radiation produced by the radiation source. The electrical sensor measures the voltage and/or current of the radiation source. It is preferred that each sterilization system or monitoring system has at least one sensor, preferably an optical sensor, and more preferred that each sterilization or monitoring system has at least one optical sensor and at least one electrical sensor.
This invention further provides a monitoring system for a radiation source, preferably for sterilization, the monitoring system comprises a sensor and a timing means. In one embodiment, this invention provides a monitoring system comprising one or more optical sensors which comprise an integrating sphere, or cosine receptor, light guide, and a spectroradiometer with or without a timing means for measuring the radiation produced by the radiation source. Alternatively, in another embodiment, this invention provides a monitoring system comprising one or more electrical sensors, which comprise voltage and/or current monitors of the electrical energy of the radiation source for producing radiation.
The sterilization system and method of this invention comprise a radiation source to sterilize products, preferably medical devices. The sterilization system and method can be used to measure the radiation to which the product is exposed. The system and method described herein are well-suited for in-line manufacturing, and will provide accurate measurements of the radiation to which a product is exposed to assure that every product receives a sterilizing dose of radiation.
The sterilization system and method, when the sensor is an optical sensor, can further be used to measure the radiation at multiple locations in the treatment area of the radiation source and provide a detailed two or three dimensional mapping of the radiation to produce a spatial distribution characterization map of the source itself. In this modality the sterilization system is used as an automated source mapping system. The maps can be used to ensure consistency from one radiation source to another to maintain uniformity in the sterilization dose in the manufacturing process.